*{
    box-sizing: border-box;
}
.calc{
    text-align: center;
    width: 232px;
    border: 1px solid #000;
    overflow: hidden;
    border-radius: 10px;
    background-color: #292a29;
    font-weight: 400
}
.calc-screen{
    height: 80px;
    line-height: 80px;
    padding: 0 10px;
    font-size: 40px;
    text-align: right;
    color: #fff;
}
.calc button{
    display: inline-block;
    width: 25%;
    height: 50px;
    line-height: 50px;
    text-align: center;
    font-size: 24px;
    border-color: #000;
    border-style: solid;
    border-width: 0 1px 1px 0;
    color: #fff;
    cursor: pointer;
}